This invention relates to a method for welding by the use of high frequency electrical resistance heating and more particularly for the welding of more or less continuous metal strips and fins or the like to metal tubes or pipes.
It has previously been known how to weld together the edges of a longitudinal gap in metal tubing as the tubing is advanced longitudinally while applying pressure thereto to close the gap at the weld point. According to the prior art method, the heating of the gap edges is effected by the use of electrodes connected to an oscillatory current source and applied respectively adjacent to the gap edges at points positioned shortly in advance of the welding point, the current being of a frequency sufficiently high so that the lowest impedance path between the electrodes follows the gap edges to and from the weld point. It has also previously been known how to provide the welding together of metal strips and metal plates by bending one of the elements out of its plane, see U.S. Pat. No. 2,821,619 issued Jan. 28, 1958 to W. C. Rudd entitled "Continuous Welding of Strips And The Like", the disclosure of which is herein incorporated by reference.
The problem of welding a very stiff metal strip to a tube by the above mentioned techniques has posed serious difficulties since the stiffness of the metal fin is such that it becomes impractical to bend the metal fin in such a manner as to create the necessary V-shaped gap. Accordingly, the present invention proposes a technique which circumvents the practical difficulties of having to significantly deform a stiff metal plate or fin in order to weld the stiff metal plate or fin to a tube by means of high frequency electrical resistance heating.